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sched: restore timer_slack_ns when resetting RT policy on fork

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Commit ed4fb6d7ef ("hrtimer: Use and report correct timerslack values
for realtime tasks") sets timer_slack_ns to 0 for RT tasks in
__setscheduler_params(). However, when an RT task with SCHED_RESET_ON_FORK
creates child threads, the children inherit timer_slack_ns=0 from the
parent. sched_fork() resets the child's policy to SCHED_NORMAL but does
not restore timer_slack_ns, leaving the child permanently running with
zero slack.

Fix this by restoring timer_slack_ns from default_timer_slack_ns in
sched_fork() when resetting from RT/DL to NORMAL policy, matching the
existing behavior in __setscheduler_params().

Note: this fix alone requires a correct default_timer_slack_ns to be
effective. See the following patch for that fix.

Fixes: ed4fb6d7ef ("hrtimer: Use and report correct timerslack values for realtime tasks")
Reported-by: Qiaoting.Lin <linqiaoting@xiaomi.com>
Signed-off-by: Guanyou.Chen <chenguanyou@xiaomi.com>
Signed-off-by: Chunhui.Li <chunhui.li@mediatek.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260522131000.1664983-2-chenguanyou@xiaomi.com
This commit is contained in:
Guanyou.Chen
2026-05-22 21:09:59 +08:00
committed by Peter Zijlstra
parent 85358f0c6d
commit 63c1a12bc0
1 changed files with 1 additions and 0 deletions
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kernel/sched/core.c
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@@ -4826,6 +4826,7 @@ int sched_fork(u64 clone_flags, struct task_struct *p)
p->policy = SCHED_NORMAL;
p->static_prio = NICE_TO_PRIO(0);
p->rt_priority = 0;
p->timer_slack_ns = p->default_timer_slack_ns;
} else if (PRIO_TO_NICE(p->static_prio) < 0)
p->static_prio = NICE_TO_PRIO(0);